The present invention relates to a method for the topographic display of interior surfaces of an object, wherein the object is laterally scanned by means of a laser beam and fluorescence induced in the process is detected as a function of the site.
Topographic or site-resolved fluorescence display is used, for example, in the medical field for the fluorescent angiography of vessel display on a body organ. For this purpose, an exogenous fluorescent dye, such as fluorescein or indocyanine green, is injected into the patient's blood stream. The fluorescence of the dye is then excited by the punctiform scanning of the organ, for example, an eye, by means of a laser beam of a suitable wavelength and is detected by a detector in a laterally site-resolved manner. In the obtained fluorescent image, the vessel structures appear light before the darker background. Vessel leakages appear as regions of increased fluorescence. A conventional fluorescence display makes it possible to very precisely determine the site of the fluorescence in the lateral direction. However, no information is obtained concerning the depth of the fluorescence.
It is therefore an object of the present invention to provide a method of the above-mentioned type by means of which a three-dimensional fluorescence display is obtained.
This and other objects are achieved according to the present invention by fluorescent images being produced not only laterally but also at different depths (z-direction) confocally. For example, 32 fluorescence images in planes of different depths can be produced. As a result, a three-dimensional data matrix of fluorescence intensities is obtained. The number of matrix elements may in each case amount to, for example, 256 in the lateral direction (x and y) and 32 in the axial direction (z), corresponding to the different sectional planes. From this total data set of fluorescence intensities, the fluorescence depth profile F.sub.r (z) of the fluorescence intensity can be extracted as a function of the depth (z) for each lateral position.
The determination of the depth of the site at which the fluorescence occurs is carried out independently of the absolute amount of the fluorescence intensity. For this purpose, the course of the fluorescence depth profile is evaluated with respect to characteristics of the curve of the fluorescence depth profile. Such characteristics may, for example, be a turning point, certain sites of the monotonous curve ascent to the maximum of the curve, the maximum of the curve itself or the like. When analyzing the individual fluorescence depth profiles, the same characteristic of the course of the curve is always analyzed in order to determine the depth at which fluorescence "starts" In a preferred manner, a scaling of the fluorescence depth profile or of the curve of this profile is carried out so that the analysis becomes independent of the absolute value of the fluorescence intensity.
According to one aspect of the present invention, the depth at which fluorescence "starts" is defined at the site at which the fluorescence for the first time exceeds a certain fraction c, for example, 80% of the maximal value of the fluorescence depth profile. The determination of the depth for each lateral site, in which the fluorescence "starts", leads to a topographic chart of the fluorescence problem and thus to a confocally achieved topography of fluorescent interior surfaces in the object. This topography can, on the one hand, be coded in gray stages and can, on the other hand, be displayed as a perspective representation. In these displays, for example, in the case of the fluorescence angiography on the fundus of the eye, the retinal vessels can be recognized as clear elevations. As a result of the visualizing of the three-dimensional surface of the fluorescent structures, a basic expansion of the fluorescence display is obtained. For example, in fluorescence angiography, vascular changes can be diagnosed. In addition, the control of the course and the evaluation of therapeutic successes can be carried out in the case of vascular diseases. By means of displaying vessel leakages, a three-dimensional function image of the vessel structure is obtained. In addition, examinations of the skin can be carried out.
A preferred use of the invention takes place in examinations on the eye, particularly on the fundus of the eye.